The overall objective of the project is to investigate hydrate system dynamics beneath seafloor mounds—a structurally focused example of hydrate occurrence at the landward extreme of their stability field—in the northern Gulf of Mexico. Researchers will conduct observatory-based in situ measurements at Woolsey Mound, MC118 to:

Characterize (geophysically) the sub-bottom distribution of hydrate and its temporal variability and,

Seafloor mounds represent one of the most diverse and least understood settings in which hydrates are found (Ahron, et al., 1992; Roberts and Aharon, 1994). Hydrate within seafloor mounds occurs as veins, nodules, and angular clasts encased in deformed, fine-grained sediment. It has also been found as massive outcroppings on the seafloor and as slabs of hydrate exposed above the seafloor. Hydrate-bearing mounds occur in water depths greater than 330m, worldwide, in association with a variety of other seafloor features including methane seeps (Crutchley et al., 2010), cold-seeps (Barnes et al., 2010), pockmarks (Chand et al., 2008), and gas chimneys.

Currently, hydrate-bearing mounds make better candidates for study than non-mound related hydrate within deformed muds, in part because mounds stand out on industry seismic data. The U.S. Bureau of Ocean Energy Management has used available industry data to identify over 2,300 potential hydrate-bearing mounds in the northern Gulf of Mexico. This project will focus on hydrate within seafloor mounds because the structurally-focused methane flux at these sites likely causes hydrate formation and dissociation processes to occur at higher rates than at sites where the methane flux is less concentrated. Furthermore, because the hydrocarbon flux at hydrate-bearing mound sites is structurally focused, these mounds may represent the exceptional case in which methane (and other hydrocarbon gases) occurs in three phases: solid hydrate, free gas, and dissolved in pore fluids. This three-phase equilibrium is very sensitive to even small environmental changes and likely causes hydrate formation and dissociation to occur at higher rates than at sites where the methane flux is less concentrated (Liu and Fleming, 2007). Hence, hydrate-bearing mounds represent the best chance of observing hydrate system dynamics in action.

Impact

Hydrate within seafloor mounds (and deformed marine muds in general) is the most likely form of marine hydrate to undergo rapid dissociation—leading to the potential release of large volumes of methane into the atmosphere—when some climatic trigger point is reached. Reliable estimates of the global volumes of methane in this setting and the conditions under which dissociation occurs are needed in order to assess the potential role shallow marine hydrate may play in climate change. This project, if successful, will shed new light on these issues by tying hydrate dynamics to oceanographic parameters that derive from and impact climate change.

Accomplishments (most recent listed first)

Researchers published a paper titled: “Seafloor Direct Current Techniques for Deep Marine, Near-bottom Gas Hydrate Investigation” in The Leading Edge.

The resistivity profiles show significant changes in the distribution of high resistivity anomalies, associated with hydrate concentration, occurred from one week to the next.

Two time-lapse DCR profiles were recovered from the instruments showing images of the near subseafloor.

The research team successfully recovered the Integrated Portable Seafloor Observatory (IPSO) lander and DCR array from the seafloor at MC118 after a 5-month deployment.

The research team successfully deployed the IPSO lander and DCR array on the seafloor at MC118.

The DCR pressure housing successfully passed high-pressure testing conducted at the Southwest Research Institute in San Antonio, Texas. The tests were conducted to determine if the pressure housing could survive the pressures that exist on the seafloor at MC118, which is located at a water depth of approximately 900 meters.

Researchers identified and ranked potential sites for the deployment of the DCR array. The primary site is supported by the recovery of hydrate during the 2011 Jumbo Piston coring effort, by the identification of a significant resistivity anomaly during the 2009 DCR survey of the mound at MC118, and by anomalously high heat flow values measured across the nearby surface trace of the fault identified in the subsurface chirp data collected in 2005.

The team constructed the IPSO lander, including installing and testing the oceanographic instruments to be deployed on the lander.

Renovations to the DCR device have been made prior to its scheduled deployment at Woolsley Mound in September 2013. Four electronic cards, damaged when the instrument housing flooded last year, were replaced. O-ring groove dimensions in the instrument housing were also verified to ensure proper seating of the rings under the pressures anticipated at the seafloor at MC118.

Current Status

(June 2015)
The project was ended on January 31, 2015 due to equipment failure. The final report is available below under "Additional Information".